Numerous types of folding wall beds, desks, tables and other pieces of furniture are known in the prior art and are widely used in situations in which available space is at a premium. The bed or other piece of furniture is provided with hinges so that it can be pivoted upwards from its generally horizontal use position to a generally vertical storage position adjacent a wall or in a small closet placed in a wall for that purpose.
Because the weight involved in even a medium sized wall bed can be considerable, it has long been considered desirable to provide some type of counterbalance springs to make it easier for a person to move the bed between the use and storage positions. The same situation exists with respect to all types of pivoting or foldup loads, including but not limited to, foldup desks, tables, work counters, loading ramps or doors hinged at the bottom, or any member pivoted near its bottom for movement between a generally vertical to a generally horizontal position. For purposes of illustration, the present invention as disclosed herein is applied to a folding wall-type bed, but it will be understood that the present invention is equally applicable to any of the pivoting type loads discussed above.
Numerous types of counterbalance mechanisms have been used in prior art foldup beds. One type of counterbalance mechanism is disclosed in U.S. Pat. No. 3,999,245 to Richard C. Bue et al, the disclosure of which is incorporated herein. The counterbalance mechanism of that patent is connected between a stationary base portion or stationary frame member and a movable frame portion. The counterbalance means includes a spring operatively connected to one of the frame members, and attached to the other of the frame members and a cable or other flexible force transmitting member interconnecting the spring and the other of the hinge frame members and passing over and around a cam surface to provide a variable effective radius and leverage arm for the spring according to the position of the hinge. Because of the unique cam, which is designed in consideration of the peripheral length of the cam surface as well as the cam effective radius, a smaller effective radius is provided when the load is in its horizontal position and a larger effective radius when the load is in its vertical or stored position.
While a counterbalance mechanism, such as disclosed in the above patent, greatly reduces the amount of force which is necessary to move a folding wall-type bed between its use and storage positions, the application of such a small force can still be burdensome to some persons. For example, when a folding bed is to be used by a seriously handicapped, invalid or extremely elderly person, the application of the manual force to pivot the bed may be undesirable. However, the use of a high powered motorized mechanism for pivoting a bed between its use and storage positions could be dangerous unless safety features could be built into such a system.